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PCI Audio SAA7785
Accelerator
Philips Semiconductors Preliminary Specification
1999 Nov 12 20
STOP# PCI Bus Stop (Target Initiated Termination)
When the SAA7785 is a PCI master, STOP# is an input which causes the SAA7785 to com-
plete, abort or retry the transfer, depending on the state of TRDY# and DEVSEL#.
When the SAA7785 is a PCI slave, it drives STOP# as active (LOW) to terminate or retry a
transaction.
TRDY# PCI Bus Target Ready
When the SAA7785 is a PCI master, TRDY# is an input which indicates the target agent’s abil-
ity to complete the data phase of the transaction. After initiation of a PCI bus transaction, the
SAA7785 inserts wait cycles until TRDY# is sampled active.
When the SAA7785 is a PCI slave, it drives TRDY# active to indicate that the SAA7785 has
sampled the data from AD[31:0] during a write phase, or presented valid data on AD[31:0] dur-
ing a read phase.
PAR PCI Bus Parity
When the SAA7785 is a PCI master, it drives PAR to reflect the correct value for even parity on
the AD[31:0] and C/BE#[3:0] buses one clock after the address phase and after each write data
phases.
When the SAA7785 is a PCI slave, it drives PAR to reflect the correct value for even parity on
the AD[31:0] and C/BE#[3:0] buses one clock after completion of each read data phase.
PCREQ# PC/PCI DMA Request
This signal requests DMA series from an external chipset that supports PC/PCI protocols. The
SAA7785 chip asserts PCGNT# according to the desired DMA channel required by either the
SoundBlaster or AC97 interfaces. The requested channel is encoded serially on the PCGNT#
pin.
The SAA7785 will become the bus owner when it receives an asserted PCGNT# signal. This
handshaking is synchronous to PCLK.
PCGNT# PC/PCI DMA Grant
An asserted PCGNT# pin indicates that the external PC/PCI master arbiter has granted DMA
services to the encoded DMA channel to the requesting DMA agent on the SAA7785 chip.
REQ# PCI Bus Request
This signal controls the PCI bus arbitration between the SAA7785 chip and the PCI master
arbiter. When REQ# is asserted, the SAA7785 indicates a desire to become the PCI bus owner.
The SAA7785 will become the bus owner when it receives an asserted grant signals (GNT# is
LOW). This handshaking is synchronous to PCLK.
REQ# is three-stated while RST# is active.